A typical computer system includes at least a microprocessor and some form of memory. The microprocessor has, among other components, arithmetic, logic, and control circuitry that interpret and execute instructions necessary for the operation and use of the computer system. FIG. 1 shows a typical computer system (10) having a microprocessor (12), memory (14), integrated circuits (ICs) (16) that have various functionalities, and communication paths (18), i.e., buses and wires, that are necessary for the transfer of data among the aforementioned components of the computer system (10).
As circuit elements continue to get smaller and as more and more circuit elements are packed onto an IC, ICs (16) dissipate increased amounts of power, effectively causing ICs (16) to run hotter. Consequently, increased operating temperatures create a propensity for performance reliability degradation. Thus, it is becoming increasingly important to know the temperature parameters in which a particular IC operates.
The temperature level in an IC is typically measured by producing a voltage proportional to temperature, i.e., a temperature-dependent voltage. It is also useful to produce a temperature-independent voltage, i.e., a voltage insensitive to temperature, that can be processed along with the temperature-dependent voltage to allow for cancellation of process variations (circuit inaccuracies introduced during the manufacturing stage) and supply variations (fluctuations in the input voltage or current of a circuit).
FIG. 2 shows a typical temperature measurement technique using a temperature-dependent and temperature-independent voltage generator (xe2x80x9cTIDVGxe2x80x9d). The TIDVG (22) resides on a portion of an integrated circuit, such as a microprocessor (20), in order to measure the temperature at the portion of the microprocessor (20) on which the TIDVG resides. The TIDVG (22) generates a temperature-dependent voltage (24) representative of the temperature and a temperature-independent voltage (26), which are used as power supplies for a voltage-to-frequency (xe2x80x9cV/Fxe2x80x9d) converter (28) (also referred to as xe2x80x9cvoltage controlled oscillatorxe2x80x9d or xe2x80x9cVCOxe2x80x9d) disposed on the microprocessor (20). The V/F converter (28) converts the temperature-dependent voltage (24) and the temperature-independent voltage (26) to frequencies that can be used by other components of the microprocessor (20).
However, this technique is prone to inaccuracy because fluctuations in the V/F converter""s (28) power supplies may adversely affect the frequencies generated by the V/F converter (28). For example, in FIG. 3, a voltage regulator (100), in this case a PMOS transistor, controls current flow to the V/F converter (28). If the power supply to the voltage regulator (100) varies due to power variations, then current flow to the V/F converter (28) also accordingly varies. If left unchecked, these power variations, known as power supply noise, can corrupt data and/or signals associated with the temperature-dependent and temperature-independent voltages (24 and 26, respectively), and may cause erroneous temperature measurements. Further, power supply noise is one of the few noise sources that cannot be nulled during calibration. Because erroneous temperature measurements can cause erroneous system behavior, e.g., unnecessary shutdown of the computer system, there is a need for reducing the amount of noise present in a V/F converter""s (28) power supplies. In other words, there is a need for a technique to increase power supply noise rejection in an on-chip temperature sensor.
According to one aspect of the present invention, an integrated circuit having a temperature sensor disposed thereon comprises a voltage generator that outputs a voltage representative of a temperature on the integrated circuit; a voltage regulator that uses feedback to decouple power supply noise from the voltage; and a voltage-to-frequency converter that generates a frequency using the voltage as a control voltage for the voltage-to-frequency converter, where the frequency is representative of the temperature.
According to another aspect, an apparatus for rejecting power supply noise on a voltage signal generated by a voltage generator comprises means for generating a differential voltage in relation to the voltage signal; means for generating an output voltage based on the differential voltage; and means for generating a buffered power supply voltage in relation to the output voltage.
According to another aspect, a method for rejecting power supply noise on a voltage signal generated by a voltage generator comprises generating an output voltage based on a differential voltage, where the output voltage is generated by an output stage; and generating a buffered power supply voltage in relation to the output voltage, where the buffered power supply voltage is generated by the output stage.
Other aspects and advantages of the invention will be apparent from the following description and the appended claims.